1. Field of the Invention
The present invention relates to an apparatus for controlling the infestation of buildings by insect pests, and, more particularly, to a pesticidal blanket which may be disposed as a liner in an excavation prior to the construction of building therein.
2. Description of the Prior Art
Insect pest control devices comprising some form of bonded textile fibers coated with an insecticide are known in the art. For example, U.S. Pat. No. 4,103,450 to Whitcomb shows an insecticidal device, which uses a lofty bonded web of textile fibers as a scaffold for insecticidal materials, which may subsequently volatilize therefrom into the ambient air. The device purports to permit control over the location, distribution and dispersal of the volatile insecticide deployed therein, and may be simply discarded when the quantity of the insecticide remaining therein falls below an effective level. The device is said to have a number of advantages, particularly for household applications, because it may be deployed readily in small spaces behind appliances which may attract insects. Because the insects in question may actually crawl through the interstices between the textile fibers in the lofty assembly, thereby coming into prolonged direct physical contact with the insecticide being used, the Whitcomb device is highly efficient in its use of the insecticide.
As may be observed, the emphasis in the Whitcomb pat is on a lofty, resilient, highly porous structure which provides an effective, but temporary, means of controlling domestic insect pests in the interior of a house. However, the solution to problems encountered in external, or outdoor, insect control requires a totally different approach. example, in many parts of the world, termites are endemic, and, as cellulose forms their principal food material, the extent of the damage that they can cause to wooden structures is well-known. Typically, termite colonies form nests underground in the soil near ground level, in a stump or other source of timber, or in the trunk of a living tree. Colonees may persist for years and may attain populations running into millions.
Termite attacks originate from the nest Timber lying on or buried, partially or completely, in the ground may be reached by underground foraging galleries. Attacks may also be carried out well above the ground surface via access passages constructed by the termites from mud or earth on a concrete or brick building foundation.
Both the building and its contents may be provided with significant protection by means of a chemical soil barrier which prevents the attacking termites from reaching wooden components. The conventional practice is to treat the soil surrounding a building foundation and footing with any one of a number of well-known chemicals. Chemicals such a aldrin, chlordane, dieldrin and heptachlor may be sprayed on the soil surface by low pressure spray equipment. Alternatively, vertical chemical barriers may be installed by excavating trenches, by treating the exposed trench and by refilling the trench with treated soil, or by rod injection.
In addition to spraying soil with toxic chemicas, other practitioners in the field have proposed insecticidal barriers, including barriers against termite for use around building structures. For example, U.S. Pat. No. 2,899,771 discloses a flexible vapor barrier carrying a layer of water-emulsifiable insecticide. The insecticide in question is carried in a flexible, relatively thin, water-soluble substance, such as "Polyox". U.S. Pat. No. 2,139,225 shows a paper which is coated with arsenate of lead mixed into a paint, whose base is mineral pitch or asphalt. A felt paper in sheet form is impregnated with the mixture by application to one or both surfaces thereof. After the paper has dried, it is packaged and thereafter may be used whenever desired in the same manner as ordinary felt paper, i.e., it ca be laid under floors, or placed between foundations and superstructures, or between the walls of buildings and roofs.
An interesting alternative approach to the provision of an effective termite barrier for new construction is described in International Patent Publication No. WO 90/14004 This publication describes a method of preventing termite damage by providing at the building site a flexible, untreated blanket which is used, for example, to line a building excavation, and then is impregnated with a suitable insecticide. The new construction is then built over the impregnated blanket. The fiber assembly is not described in great detail in this publication. In particular, International Patent Publication No. WO 90/14004 teaches nothing about the fiber density of the fiber assembly, or about its void volume.